We have never had the money or room for either but I need a new washer anyway.
I don't think I'd use the dishwasher however if I got the drier I wouldn't need to have the airer in the kitchen. Obviously most washer / driers are double the cost of a washer on its own.
My parents had a dryer over 20 years ago and I remember my dad saying they cost a lot to run.
Are either worth it?